Collaborative Research: The Effect of Atmospheric Humidity on the Susceptibility of Dry Soils to Wind Erosion

风蚀是干旱半干旱地区普遍存在的风蚀过程，造成土壤肥力损失、大气辐射改变和大气污染，对全球和区域气候、农业和人类健康具有重要影响。当风速超过一定阈值时，就会发生侵蚀，而风速的值取决于许多因素，包括表层土壤湿度。作者认为，在干旱区，在空气干燥的条件下，地表土壤水分的变化会受到大气湿度变化的显著影响，并对风蚀潜力产生重要影响，而这种影响目前还没有得到很好的理解或量化。实际上，土壤湿度对风蚀易感性的影响在土壤湿度的气干范围内与在毛管范围内相反，即空气干燥的土壤越干燥，其对风蚀的易感性越低。拟议中的研究将检验这一假设，并通过分析美国几种重要的农业土壤（这些土壤极易受到风蚀）以及分类良好、干净的沙子（将作为“参考”土壤）来量化其影响。具体而言，该项目将(1)研究表层土壤水分（即几个粮食层）对空气湿度和温度的依赖；(2)通过多次风洞试验确定阈值风速与近地面空气湿度和温度之间的关系；(3)用理论框架解释结果，该框架将考虑粒子间力对吸收层结合的依赖、粒子间力和土壤基质势的依赖。这种方法将提供一个理论方程，表示空气干燥土壤的阈值风速作为空气湿度的函数。该方程的参数将通过风洞实验结果确定。评估土壤侵蚀潜力与地表含水量之间存在的依赖类型对旱地景观风蚀和沙尘排放的理解和建模至关重要。知识价值。现有的表面湿度对阈值风速影响的研究大多集中在相对湿润的土壤上，其中毛细作用主导着颗粒间的结合力。该方案认识到干性土壤作为干旱地区大气粉尘和风蚀源的重要性。在这些土壤中，含水量对颗粒间结合的贡献主要是吸附层结合。该方案认识到液桥结合（毛细作用）和吸附层结合对土壤含水量的不同依赖，并研究了它们如何影响土壤可蚀性和表面水分之间的关系。此外，由于地表土壤湿度测量很少，因此将研究地表土壤湿度对空气湿度的依赖关系，并用于预测土壤的可蚀性状态。据我们所知，这是为数不多的集中研究空气干燥土壤可蚀性的研究之一，也是第一个显示可蚀性增加与水分含量增加有关的研究。利用空气湿度作为地表土壤湿度的替代物，也是研究土壤侵蚀潜力的水文控制的一种独特而新颖的方法。更广泛的影响本项目将包括对一名博士生和两名高中科学教师进行研究方法和研究成果展示方面的培训。它将通过整合到pi正在开发的课程中来支持教育，并为研究类似问题的不同小组之间的合作提供基础。将寻求代表性不足群体的成员加入研究小组。拟议的研究结果将通过学术期刊的出版物和会议发言加以传播。社会将受益于对风蚀和粉尘产生的原因的进一步了解和预测能力的提高。

ABSTRACTWind erosion is a widespread process in arid and semi-arid regions, and contributes to loss of soil fertility, alteration of atmospheric radiation, and air pollution, with important impacts on global and regional climates, agriculture, and human health. Erosion occurs when wind speed exceeds a certain threshold, the value of which depends on a number of factors, including surface soil moisture. It is argued that in arid regions, under air-dry conditions, variations in surface soil moisture can be significantly affected by changes in atmospheric humidity, with an important effect on wind erosion potential, and that this effect is not currently well understood or quantified.It is argued that in fact the effect of soil moisture on susceptibility to wind erosion is opposite in the air-dry range of soil moistures to its effect in the capillary range, i.e., that the drier an air-dry soil is, the less susceptible it is to wind erosion. The proposed research will test this hypothesis and quantify the effect by analysis of several important agricultural soils of the United States, which are strongly subject to wind erosion, as well as well-sorted, clean sands, which will function as "reference" soils. In particular, the project will (1) investigate the dependence of surface soil moisture (i.e., in a few grain layer) on air humidity and temperature; (2) determine the relationship between threshold wind velocity, and near surface air humidity and temperature by means of a number of wind tunnel tests, and (3) interpret the results in terms of a theoretical framework that will account for the dependence of interparticle forces on absorbed layer bonding on interparticle forces and soil matric potential. This approach will provide a theoretical equation expressing threshold wind velocity as a function of air humidity for air-dry soils. The parameters of this equation will be determined through the results of the wind tunnel experiments. The assessment of the type of dependence existing between soil erosion potential and surface moisture content is crucially important to the understanding and modeling of wind erosion and dust emission from dryland landscapes.Intellectual Merit.Most of the existing studies on the effect of surface moisture on the threshold wind velocity have concentrated on relatively wet soils, in which capillarity dominated interparticle bonding forces. This proposal recognizes the importance air-dry soils as sources of atmospheric dust and wind erosion in dryland landscapes. In these soils, water content contributes to interparticle bonding mostly as adsorbed-layer bonding. The proposal recognizes the different dependence of liquid-bridge bonding (capillarity) and adsorbed-layer bonding on soil water content, and investigates how it affects the relationship between soil erodibility and surface moisture. Moreover, because surface soil moisture measurements are seldom available, the dependence of surface soil moisture on air humidity will be investigated and used to predict the state of soil erodibility. To our knowledge, this is one of the very few studies concentrating on the erodibility of air-dry soils and the first one showing an increased erodibility associated with increasing moisture contents. The use air humidity as a surrogate for surface soil moisture conditions is also a unique and novel approach to the study of the hydrologic controls on soil erosion potential.Broader ImpactsThis project will involve the training of a Ph.D. student, and two high school science teachers in the methods of research and of presentation of research results. It will support education by integration into a course being developed by the PIs, and provide a basis for collaboration between different groups working on similar questions. Members of underrepresented groups will be sought for inclusion in the research team. The results of the proposed research will be disseminated through publications in scholarly journals and conference presentations. Society will benefit from the improved understanding of the causes of and the ability to predict wind erosion and dust generation.